Algebraic computation of some intersection D-modules

Let $X$ be a complex analytic manifold, $D\subset X$ a locally quasi-homogeneous free divisor, $E$ an integrable logarithmic connection with respect to $D$ and $L$ the local system of the horizontal sections of $E$ on $X-D$. In this paper we give an algebraic description in terms of $E$ of the regular holonomic D-module whose de Rham complex is the intersection complex associated with $L$. As an application, we perform some effective computations in the case of quasi-homogeneous plane curves.Comment: 18 page

Free initial wave packets and the long-time behavior of the survival and nonescape probabilities

The behavior of both the survival S(t) and nonescape P(t) probabilities at long times for the one-dimensional free particle system is shown to be closely connected to that of the initial wave packet at small momentum. We prove that both S(t) and P(t) asymptotically exhibit the same power-law decrease at long times, when the initial wave packet in momentum representation behaves as O(1) or O(k) at small momentum. On the other hand, if the integer m becomes greater than 1, S(t) and P(t) decrease in different power-laws at long times.Comment: 4 pages, 3 figures, Title and organization changed, however the results not changed, To appear in Phys. Rev.

Full time nonexponential decay in double-barrier quantum structures

We examine an analytical expression for the survival probability for the time evolution of quantum decay to discuss a regime where quantum decay is nonexponential at all times. We find that the interference between the exponential and nonexponential terms of the survival amplitude modifies the usual exponential decay regime in systems where the ratio of the resonance energy to the decay width, is less than 0.3. We suggest that such regime could be observed in semiconductor double-barrier resonant quantum structures with appropriate parameters.Comment: 6 pages, 5 figure

Time scale of forerunners in quantum tunneling

The forerunners preceding the main tunneling signal of the wave created by a source with a sharp onset or by a quantum shutter, have been generally associated with over-the-barrier (non-tunneling) components. We demonstrate that, while this association is true for distances which are larger than the penetration lenght, for smaller distances the forerunner is dominated by under-the-barrier components. We find that its characteristic arrival time is inversely proportional to the difference between the barrier energy and the incidence energy, a tunneling time scale different from both the phase time and the B\"uttiker-Landauer (BL) time.Comment: Revtex4, 14 eps figure

Impacts of land grabbing and agribusiness on peasant family farming in the province of Los Ríos – Ecuador

Land grabbing and agribusiness have generated serious implications for the sustainability of peasant communities in the global south. This paper analyzes perceptions of the impact of land grabbing and agribusiness on peasant family farming in three cantons of Los Ríos Province in Ecuador, using focus groups in 2020. The sustainable development framework and content analysis using NVIVO12 software were used. In the territories, negative impacts were mostly identified that seriously compromise their sustainable development, given that monocultures and the agribusiness production system have had strong implications in deforestation, loss of biodiversity, contamination of natural resources, modification of the agricultural landscape, and farmers’ health. Keywords: land grabbing, peasants, agribusiness. Resumen El acaparamiento de tierras y los agronegocios han generado serias implicaciones en la sostenibilidad de comunidades campesinas del sur global. En este artículo se analizan las percepciones del impacto del acaparamiento de tierras y los agronegocios en la agricultura familiar campesina en tres cantones de la Provincia de Los Ríos en Ecuador, aplicando grupos focales en el 2020. Se empleó el marco del desarrollo sostenible y el análisis de contenidos mediante el software NVIVO12. En los territorios se identificaron mayoritariamente impactos negativos que comprometen seriamente su desarrollo sostenible, dado que los monocultivos, sistema de producción de los agronegocios, han tenido fuertes implicaciones en la deforestación, pérdida de biodiversidad, contaminación de recursos naturales, modificación paisaje agrícola y salud de los agricultores. Palabras Clave: acaparamiento de tierras, campesinos, agronegocios

Sistema para el control de acceso a un centro comercial

Sequential logic systems over the years have allowed an improvement in control and access systems. This article looks for a way to use this type of logic to create an autonomous system in Verilog for the access of people to a shopping mall, which should allow the realization of counts, movement analysis, and temperature detections, which allow avoiding the direct relationship with the security employees, making this way a protection measure for situations like the one that is currently being experienced with the global pandemic. This system, due to its configuration and accessibility, must be easy to understand, therefore the operation of this project is visualized with a traffic light configuration where green represents a positive action of entry, represents an alert or emergency. The system will give a stop signal, either for high temperatures or for people over or equal to the limits.Los sistemas de lógica secuencial a lo largo de los años han permitido un mejoramiento en los sistemas de control y de acceso. Este artículo busca la manera de usar este tipo de lógica para crear un sistema autónomo en Verilog de acceso de personas a un centro comercial, el cual debe permitir la realización de conteos, análisis de movimiento y detecciones de temperatura, que permitan evitar la relación directa con los empleados de seguridad haciendo de esta forma una medida de protección para situaciones como la que se está viviendo actualmente con la pandemia mundial. Este sistema, debido a su configuración y accesibilidad, debe ser de fácil comprensión, por esto el funcionamiento de este proyecto se visualiza con una configuración de semáforo en donde el verde representa una acción positiva de ingreso, mientras que el rojo representa una alerta o emergencia.&nbsp

Composite Spin Waves, Quasi-Particles and Low Temperature resistivity in Double Exchange Systems

We make a quantum description of the electron low temperature properties of double exchange materials. In these systems there is a strong coupling between the core spin and the carriers spin. This large coupling makes the low energy spin waves to be a combination of ion and electron density spin waves. We study the form and dispersion of these composite spin wave excitations. We also analyze the spin up and down spectral functions of the temperature dependent quasi-particles of this system. Finally we obtain that the thermally activated composite spin waves renormalize the carriers effective mass and this gives rise to a low temperature resistivity scaling as T ^{5/2}.Comment: 4 pages, REVTE

SPITZER: Accretion in Low Mass Stars and Brown Dwarfs in the Lambda Orionis Cluster

We present multi-wavelength optical and infrared photometry of 170 previously known low mass stars and brown dwarfs of the 5 Myr Collinder 69 cluster (Lambda Orionis). The new photometry supports cluster membership for most of them, with less than 15% of the previous candidates identified as probable non-members. The near infrared photometry allows us to identify stars with IR excesses, and we find that the Class II population is very large, around 25% for stars (in the spectral range M0 - M6.5) and 40% for brown dwarfs, down to 0.04 Msun, despite the fact that the H(alpha) equivalent width is low for a significant fraction of them. In addition, there are a number of substellar objects, classified as Class III, that have optically thin disks. The Class II members are distributed in an inhomogeneous way, lying preferentially in a filament running toward the south-east. The IR excesses for the Collinder 69 members range from pure Class II (flat or nearly flat spectra longward of 1 micron), to transition disks with no near-IR excess but excesses beginning within the IRAC wavelength range, to two stars with excess only detected at 24 micron. Collinder 69 thus appears to be at an age where it provides a natural laboratory for the study of primordial disks and their dissipation.Comment: ApJ, in pres

YSOVAR: Six pre-main-sequence eclipsing binaries in the Orion Nebula Cluster

Eclipsing binaries (EBs) provide critical laboratories for empirically testing predictions of theoretical models of stellar structure and evolution. Pre-main-sequence (PMS) EBs are particularly valuable, both due to their rarity and the highly dynamic nature of PMS evolution, such that a dense grid of PMS EBs is required to properly calibrate theoretical PMS models. Analyzing multi-epoch, multi-color light curves for 2400 candidateOrion Nebula Cluster (ONC) members from our Warm Spitzer Exploration Science Program YSOVAR, we have identified 12 stars whose light curves show eclipse features. Four of these 12 EBs are previously known. Supplementing our light curves with follow-up optical and near-infrared spectroscopy, we establish two of the candidates as likely field EBs lying behind the ONC. We confirm the remaining six candidate systems, however, as newly identified ONC PMS EBs. These systems increase the number of known PMS EBs by over 50% and include the highest mass (Theta1 Ori E, for which we provide a complete set of well-determined parameters including component masses of 2.807 and 2.797 solar masses) and longest period (ISOY J053505.71-052354.1, P \sim 20 days) PMS EBs currently known. In two cases (Theta1 Ori E and ISOY J053526.88-044730.7), enough photometric and spectroscopic data exist to attempt an orbit solution and derive the system parameters. For the remaining systems, we combine our data with literature information to provide a preliminary characterization sufficient to guide follow-up investigations of these rare, benchmark systems.Comment: Accepted by Ap

Conductance as a Function of the Temperature in the Double Exchange Model

We have used the Kubo formula to calculate the temperature dependence of the electrical conductance of the double exchange Hamiltonian. We average the conductance over an statistical ensemble of clusters, which are obtained by performing Monte Carlo simulations on the classical spin orientation of the double exchange Hamiltonian. We find that for electron concentrations bigger than 0.1, the system is metallic at all temperatures. In particular it is not observed any change in the temperature dependence of the resistivity near the magnetical critical temperature. The calculated resistivity near $T_c$ is around ten times smaller than the experimental value. We conclude that the double exchange model is not able to explain the metal to insulator transition which experimentally occurs at temperatures near the magnetic critical temperature.Comment: 6 pages, 5 figures included in the tex